Core wire for multi-core cables and multi-core cable

Abstract

A core wire for multi-core cables includes a conductor obtained by twisting a plurality of elemental wires, and an insulating layer coated on an outer peripheral surface of the conductor. The insulating layer contains polyethylene-based resin as a main component, and the product of a linear expansion coefficient C1 of the insulating layer in the range of 25° C. to −35° C. and an elastic modulus E1 at −35° C., namely (C1×E1) is 0.01 MPaK−1 or more and 0.90 MPaK−1 or less. The melting point of the polyethylene-based resin is 80° C. or higher and 130° C. or lower.

The invention claimed is: 
     
       1. A core wire for multi-core cables comprising:
 a conductor obtained by twisting a plurality of elemental wires; and 
 an insulating layer coated on an outer peripheral surface of the conductor, the insulating layer containing polyethylene-based resin as a main component, the polyethylene-based resin being at least one selected from a group consisting of high-density polyethylene and low-density polyethylene, wherein:
 a product of a linear expansion coefficient C1 of the insulating layer in a range of 25° C. to −35° C. and an elastic modulus E1 at −35° C., namely (C1×E1) is 0.01 MPaK −1  or more and 0.90 MPaK −1  or less, and 
 a melting point of the polyethylene-based resin is 80° C. or higher and 130° C. or lower. 
 
 
     
     
       2. The core wire for multi-core cables according to  claim 1 , wherein the insulating layer has an elastic modulus E2 of 100 MPa or more at 25° C. 
     
     
       3. The core wire for multi-core cables according to  claim 1 , wherein the insulating layer has a second linear expansion coefficient C2 of 5.0×10 −4  K −1  or less in a range of 25° C. to 80° C. 
     
     
       4. The core wire for multi-core cables according to  claim 1 , wherein an average area of the conductor in a cross section is 1.0 mm 2  or more and 3.0 mm 2  or less. 
     
     
       5. The core wire for multi-core cables according to  claim 1 , wherein:
 an average diameter of the plurality of elemental wires in the conductor is 40 μm or more and 100 μm or less, and 
 a number of the plurality of elemental wires is 196 or more and 2450 or less. 
 
     
     
       6. The core wire for multi-core cables according to  claim 1 , wherein the conductor is formed by twisting a plurality of wire strands, each of plurality of wire strands is obtained by twisting multiple elemental wires of the plurality of elemental wires. 
     
     
       7. A multi-core cable comprising:
 a cable core formed by twisting a plurality of core wires; and 
 a sheath layer provided around the cable core, 
 at least one of the plurality of core wires being the core wire according to  claim 1 . 
 
     
     
       8. The multi-core cable according to  claim 7 , wherein at least one of the plurality of core wires is a core wire strand which is formed by twisting multiple core wires of the plurality of core wires.